Aug. 20, 2009, was the 40th anniversary of the establishment of Florissant Fossil Beds National Monument, a site maintained by the National Park Service for the preservation of spectacular plant and insect fossils, including huge petrified trunks of fossil sequoias, ancient relatives of the giant redwoods of California. The site is located west of Colorado Springs, just south of the town of Florissant, Colo. The efforts to save the site and its paleontologic treasures from being overrun by real estate development in the 1960s is a dramatic story that was retold by speakers during the anniversary celebration.

The rocks and fossils of Florissant date back 34 million years, to the end of the Eocene Epoch of geologic time. In those days, a stream flowed south through a valley west of Pikes Peak, while active volcanoes were erupting intermittently to the west. The climate was warm, and a lush forest grew on the slopes of the valley. A great variety of trees lived in the forest, many of them ancestral species of trees of today, but most prominent were sequoias with trunks tens of feet in diameter. Smaller plants bloomed beneath the trees, and early mammals roamed about, even as clouds of ash were blown skyward from time to time by nearby volcanoes. Then, abruptly, a major eruption spewed lava that flowed across the southern end of the valley, damming the stream. A large lake quickly formed, filling the valley.

As the volcanoes continued to erupt, ash and mud flowed down the slopes of the valley into the lake, engulfing the bases of the sequoias. The huge trees died, and their upper parts, still standing in the water of the lake, disintegrated, but the lower parts of the trunks became fossilized — petrified — as minerals soaked into the cells of the wood.

Meanwhile, on the valley slopes and at the margins of the lake, vegetation continued to grow, despite periodic falls of volcanic ash and dust. Leaves and flowers of these plants sank to the bottom of the lake and were gently buried by layers of ash. Also buried and magnificently preserved were myriads of insects that had been crawling or flying about but then were washed into the lake. These small but exquisite fossils, along with the giant sequoia stumps, are the treasures preserved today in the paper-thin layers of shale at Florissant Fossil Beds National Monument.

Just how the fossil heritage of the monument was conserved for scientific study and enjoyment today, against an imminent threat of bulldozers and summer homes, was recounted during the 40th anniversary celebration. In the mid-1960s, a group of concerned citizens and scientists was organized, the Defenders of Florissant. Prominent in this group was Dr. Estella Leopold, a paleobotanist and daughter of pioneering environmentalist and conservationist Aldo Leopold (author of “A Sand County Almanac”). Senate bills and court cases were presented to save the site for the public. Dr. Leopold spoke at the anniversary celebration, as did lawyer Victor Yannacone from New York and Richard Lamm, then a young lawyer and later governor of Colorado, recalling their roles in the struggle. They had argued the site should be ceded to the National Park Service for permanent protection. Lawsuits were filed and denied, but reintroduced. Eventually Congress agreed, and finally in August 1969, Pres. Richard Nixon signed the bill. A new national monument was created, and 1,700 species of fossil plants and insects were saved.

In the next “Our Natural World” column, more details about the fossils of Florissant. To learn more in the meantime, visit www.NPS.gov/flfo/index.htm.

Doug Nichols is a Scientist Emeritus with the U.S. Geological Survey and a Research Associate with the Denver Museum of Nature & Science. He is a resident of Berthoud. Send comments to recorder.science.guy@gmail.com.